It is well known that production from oil and gas wells can suffer due to the build-up of fluids at the bottom of the well. Various methods and devices have been developed to remove those fluids so as to improve the well's productivity. See e.g., U.S. Pat. No. 6,148,923, which is incorporated herein by reference.
One such device is known as a plunger, of which there are many variants known to those skilled in the art. For example, an auto-cycling plunger operates as follows: (1) it is dropped into the well (at the well's surface); (2) it free-falls down the well until it stops upon impact at the bottom of the well; and (3) it thereafter is caused (by pressure in the well) to travel back toward the surface of the well, pushing a “load” of liquid above it for removal at the well's surface by a lubricator assembly. The plunger then is allowed to repeat that cycle, thereby ultimately removing enough fluid from the well to improve its production.
A number of problems have arisen from the use of prior art plungers. For example, due to the typically great distance between the surface and bottom of a well, and high pressures within the well system, the plunger often travels at a great rate of speed when it is received by the lubricator at the top of the well and/or received by a bumper assembly at the bottom of the well. Impacts between the plunger and the lubricator and/or bumper assembly can be violent. They often are so violent that damage occurs (either immediately or over time due to repeated use) to the lubricator, the bumper assembly, and/or the plunger itself.
Additionally, components of the plunger may be susceptible to damage from repeated use or adverse use conditions. For example, a shuttle ball plunger may include a shuttle ball that is configured to insert into an opening in the plunger, thereby closing the plunger to fluid flow and causing the plunger to rise to the surface of the well. The fluid found in the well typically includes dirt, grime, and other debris, which can cause excess wear to surfaces interfacing between the shuttle ball and the plunger body.
Still further, some shuttle ball plungers include an o-ring retention mechanism for retaining the shuttle ball within the opening of the plunger until the plunger rises to the wellhead and the shuttle ball is ejected (against the force exerted by the o-ring) from the plunger by the lubricator system. Other shuttle ball plungers include a metal c-clip having square or rectangular edges for receiving and then holding the shuttle ball in place until the plunger reaches the lubricator. It has been discovered, however, that after repeated high energy use, these retention mechanisms either failed due to wear and/or (in the case of the metal c-clip having square edges) damaged the interior side walls of the plunger, thereby limiting the useful life of the plunger assembly in both cases.